fwrite(): Write of 2 bytes failed with errno=22

[forenkema]

I have a PHP application which uses piphp. This worked fine on a Raspberry 4. However, after migrating to Raspberry 5, I get the exception: fwrite(): Write of 2 bytes failed with errno=22:

1. in /var/www/basic/vendor/piphp/gpio/src/FileSystem/FileSystem.phpat line 55
46474849505152535455565758596061626364        
$this->exceptionIfFalse($bytesWritten, $extra);
 
        return $bytesWritten;
    }
 
    private function exceptionIfFalse($result, $extra = '')
    {
        if (false === $result) {
            $errorDetails = error_get_last();
            throw new RuntimeException($errorDetails['message'].' '.$extra);
        }
    }
 
    /**
     * {@inheritdoc}
     */
    public function exists($path)
    {
        return file_exists($path);
2. in /var/www/basic/vendor/piphp/gpio/src/FileSystem/FileSystem.php at line 46– PiPHP\GPIO\FileSystem\FileSystem::exceptionIfFalse()
40414243444546474849505152    
{
        $stream = $this->open($path, 'w');
 
        $bytesWritten = @fwrite($stream, $buffer);
        fclose($stream);
        $extra = $path.' '.$buffer;
        $this->exceptionIfFalse($bytesWritten, $extra);
 
        return $bytesWritten;
    }
 
    private function exceptionIfFalse($result, $extra = '')
    {
3. in /var/www/basic/vendor/piphp/gpio/src/Pin/Pin.php at line 166– PiPHP\GPIO\FileSystem\FileSystem::putContents()
160161162163164165166167168     
     *
     * @param string $file The file to write to
     */
    private function writePinNumberToFile($file)
    {
        //echo "file is $file";
        $this->fileSystem->putContents($file, $this->getNumber());
    }
}
4. in /var/www/basic/vendor/piphp/gpio/src/Pin/Pin.php at line 62– PiPHP\GPIO\Pin\Pin::writePinNumberToFile()
56575859606162636465666768     */
    public function export()
    {
        if (!$this->isExported()) {
            $this->exported = true;
 
            $this->writePinNumberToFile($this->getFile(self::GPIO_FILE_EXPORT));
 
            // After export, we need to wait some time for kernel to report changes.
            usleep(200 * 1000);
        }
    }

Debugging shows that the $file = /sys/class/gpio/export and the $buffer = 16. Both seem totally fine to me....

My user (www-data) is in the gpio group (and in the root group). So I believe that file-permissions are not the issue.

Looking around on the internet, it appears that fwrite() errno 22 is caused by writing too much data to a file. That does not seem applicable here, as /sys/class/gpio/export seems to be an emulated file (Is that right? I am not sure).